Study on multi-scale damage and failure mechanism of rock fracture penetration: experimental and numerical analysis

In natural rock masses, joints or fractures usually occur at different penetrations. To study the deformation and failure behavior of rock mass with different fracture penetrations, a series of triaxial compression experiments were conducted on rock specimens containing prefabricated fracture at penetrations of 0%, 25%, 50%, 75% and 100%. The results show that the greater the fracture penetration and the smaller the strength of the rock sample, the more obvious the plastic deformation section of the stress-strain curve. Confining pressure can greatly improve the compressive strength of rock samples. For intact rock samples, confining pressure will change the failure mode from tensile failure to shear failure. For fractured rock samples, the confining pressure will aggravate the degree of damage to the rock sample. PFC 3D simulation shows that the failure process of rock samples is accompanied by the transformation of strain energy to damping energy and particle sliding energy, which can quantitatively characterise the damage process of rock. The increasing trend of crack number is slow-steep-slow, which is the 'S' type. It began to grow rapidly after reaching peak strength and gradually stabilised after reaching residual strength. It is consistent with the trend of energy change. The article carried out multi-scale experimental study of fractured rock mass with the same length and different penetration. The larger the fracture penetration, the lower the strength of the rock sample, and the more complex the crack when it is destroyed.The article analysed and summarised the mechanical properties and failure modes of rock samples with different fissures under different confining pressures and clearly recognised the deterioration effect of fissure penetration on rock samples.PFC 3D was used to simulate the test, which clearly showed the crack propagation process of fractured rock samples under triaxial compression, quantitatively characterised the damage law and revealed the failure mechanism.